Fabrication of integrated circuits and other structures involves sequential deposition of layers of insulating, semiconducting, and conducting materials on a substrate. Adhesion properties of adjacent layers in structures are of great importance to ensure structural integrity and reliability. Poor and/or weak adhesion properties in these structures can be caused by containments at the interface between adjacent layers. For example, in structures formed using chemical vapor deposition (CVD), atomic layer deposition (ALD), or chemical fluid deposition (CFD), contaminants, such as contaminants derived from ligands, fluorine, and other contaminating materials released during the deposition process, can deposit at the interface and interfere with adhesion of a newly deposited layer. Other contaminants, such as oxides formed on the substrate and/or the deposited layer can also contribute to poor adhesion.
One method for improving the adhesion of a metal layer to a substrate surface involves the use of self-assembled monolayers of mercapto-propyl-trimethoxy-silane, e.g., as described by Ramanath and co-workers in Self-Assembled Subnanolayers as Interfacial Adhesion Enhancers and Diffusion Barriers for Integrated Circuits, 83(2): 383-85, 2003. The self-assembled monolayers (SAMs) are applied to the substrate prior to physical vapor deposition of the metal layer. The SAMs act as a coupling agent (e.g., as an adhesive) to bind the metal layer to the substrate. The increased adhesion properties in these structures rely on the presences and the stability of the SAMs at the interface. However, the presence of the SAMs, due to their non-conductive nature, can also have deleterious effects on the electronic performance of the structure.
Another method for improving the adhesion of a metal layer to a substrate surface involves the use of alternating layers of polyethyleneimine (PEI) and polyacrylic acid (PAA) as binding agents between the substrate surface and the deposited metal layer. Like the method involving the SAMs described above, the alternating layers of PEI and PAA remain within the structure after the deposition of the metal layer (e.g., the alternating layers of PEI and PAA are sandwiched between the substrate and the metal layer) and can effect the electronic performance of the structure.